Summary: We have continued our efforts to explore the multifaceted functions of nitric oxide (NO) in human physiology and its potential therapeutic values. Data generated from our collaborative studies with NIDDK, NIH on the effect of NO on the oxygen carrying and redox properties of red blood cells from sickle cell patients have now been completed and published. In these studies we have shown that treatment of blood from normal and sickle cell anemia patients with 80 p.p.m. NO gas, or with NO donor compounds, such as sodium 2-(N, N-diethylamino)-diazenolate-2-oxide (DEANO) or S-nitrosocysteine (CysNO) produced changes in the oxygen affinity, coupled with increased methemoglobin levels in both normal and sickle cells (Hrinczenko et al., Br J Haemat 110:412-419, 2000). To better understand the mechanism of how NO affects the oxygen affinity of hemoglobin we investigated the underlying kinetics that drives the reactivity of NO with hemoglobin using the stopped-flow technique. We showed in these rapid kinetics experiments that HbA, AA, or SS erythrocytes when mixed with CysNO or DEANO underwent biphasic time courses indicative of heme oxidation followed by reductive nitrosylation. Hemolysates treated with CysNO showed by electrospray mass spectroscopy a peak corresponding to a 29 mass unit increase (consistent with NO binding) of both beta(A) and beta(S) chains but not the alpha chains. We concluded that therapeutic use of NO in sickle cell disease may ultimately require further optimization of these competing reactions, i.e., heme reactivity (nitrosylation or oxidation) versus direct nitrosation of hemoglobin on the beta-globin (Hrinczenko et al., Biochem Biophys Res Comm 275:962-967, 2000). We have also reported that the delivery of NO to platelets from sickle cell patients has varying effects upon platelets responses, and that utilization of a more effective delivery method system may ultimately contribute to reducing platelet activation in sickle cell patients (Br J Haemat, in press).